Endoluminal medical prostheses are devices placed inside a duct of a living body for the treatment of certain vascular deformations such as aneurism. They often are implanted by an endoluminal route, but in other cases may be implanted via vessel stripping. When implanted endoluminally, the prosthesis may be implanted using a balloon which i inflated in the implantation duct, thereby causing the stent to be dilated plastically in order to press against the walls of the duct.
Various vascular prostheses are known in the prior art. A vascular prosthesis may comprise a frame, a flexible sleeve, and attaching or connecting mean between the sleeve and the frame. The frame is defined by one or more tubular sections arranged along at least one axis, with the sections comprising a relatively rigid meandering or undulating structure. The meandering structures of the tubular sections are coiled or wound in one or more coiling levels and have apices between which elongate segments extend.
FIGS. 1-6 illustrate the construction of the frames of various prior art protheses. FIG. 1 shows a prior art prosthesis having a frame 1 comprising a plurality of meandering or undulating structures 3, 5, 7, and 9. The meandering structures 3, 5, 7, and 9 may be made from a relatively rigid material such as a stainless steel or Nitinol.RTM. wire.
The prior art device of FIG. 1 may be constructed as illustrated in FIG. 2. The meandering structures 3, 5, 7, and 9 are formed with substantially V-shaped undulation or meanders having rounded apices 11, and after every four peaks, for example, there is a rectilinear segment 12 that is substantially twice the length of the rectilinear segments 14 which form the meanders or undulations. The wires 3, 5, 7, and 9 are juxtaposedly offset along a series of directrix lines that are oriented substantially perpendicularly to the axis 21 of the completed frame 1. The meandering structures 3, 5, 7, and 9 are welded together in pairs at points 23 (depicted as short, slanted lines across the wires 3, 5, 7, and 9 in FIG. 2) where two adjacent meandering structures lie side-by-side.
After thus producing a flat structure, the structure is coiled or wound on itself to form a tubular structure, and the segments of meandering (such as those marked 25a and 25b for level 13) located at the end of each wire 3, 5, 7, or 9 are welded to each other. There is thus obtained the stepped structure shown in FIG. 1, which is composed of the four tubular sections 13, 15, 17, and 19 connected together by the double length segments 12.
The prior art prosthesis in FIG.3 is a bifurcated prosthesis 10 comprising a principle section 27 to which two secondary branches or sections 29 and 31 are connected. The prior art device of FIG. 3 may be constructed as shown in FIG. 4, with the manufacture being nearly identical to that of the non-bifurcated device as illustrated in FIG. 2. The difference between the manufacture of the two can be seen at regions 33, where two substantially rectilinear segments of the structural wires 3, 5, 7, and 9 are not welded together, although they are still arranged side-by-side. It is the lack of intimate connection between the wires 5 and 7 at the levels marked 17a and 19a that allows one to form the two secondary branches 29 and 31 extending from the bifurcation zone 35.
FIG. 5 shows a monotube prosthesis constructed in accordance with U.S. Pat. No. 5,405,377, which is incorporated herein by reference. This prosthesis is formed from a single structural wire which is relatively rigid and resilient. The wire may be made from metal such as stainless steel, tental, or titanium, or it may be made from plastic having sufficient rigidity and resiliency to be twisted and subsequently coiled. The wire is twisted and subsequently coiled to form a continuous helix comprised of a series of loops connected at their apices to one another by small rings 41. The rings 41 connect all of the adjacent apices, e.g., 38a and 38b, of the zigzags formed by the wire 38.
Another prior art prosthesis is illustrated in FIG. 6. This prosthesis is disclosed in EP-A-540 290, which is incorporated herein by reference. The frame of the prosthesis, which consists of a tubular stent of constant circular cross-section, is a one piece unit produced from a thin metal plate by chemical erosion. It is thus possible to form a structure 43 having a series of windings at adjacent levels connected together, such as 47 and 49 or 49 and 51, by bridges of material 53 oriented parallel to the axis 55 of the completed frame 1.
The flexible sleeve of the prosthesis, which is substantially coaxial with the frame, channels a fluid which circulates in the duct of the body. The attaching means comprises at least one flexible thread which attaches the flexible sleeve to the frame. The flexible thread is not as rigid as the segments of the meandering structure and is arranged in such a manner that it wraps around at least one segment and passes through the sleeve to ensure the attachment.
One example of prostheses of this type is shown in EP-A-686 379. Other examples may be found, for example, in EP-A-540 290, WO-A-95/26 695, and WO-A-94/17754, each of which discloses a frame having several substantially coaxial coiling levels. The coiling levels are formed individually by a relatively rigid structure having meanders which include elongate segments, with the various levels being staggered and connected to one another successively, in pairs, by at least one of the structural segments.
In WO-A-95/21 592 and FR-A-2 707 434, the frame is constructed so as to form a bifurcated prosthesis. The frame comprises a principal tubular section and two secondary tubular sections connected to the principal tubular section at a substantially Y-shaped connection zone.
In prior art prostheses having fluid duct sleeves, such as those disclosed in EP-A-539 273 and in WO-A-95/26 695, certain deficiencies relating to the attachment of the sleeve to the frame have been noted. In EP-A-539 237, for example, the sleeve is attached to the frame by suture threads, made from nonbiodegradable material, which pass through the sleeve and are knotted around a structural segment of the frame to form small individual sutures. This is, however, only a punctuate connection, which is fairly time-consuming to produce, and the distance between two individual sutures has proven in practice to be fairly great. This distance may prove detrimental, especially if a suture becomes undone or torn, thus allowing the sleeve to "float" relative to the frame.